playbin之autoplug_factories源碼剖析

?一、autoplug_factories_cb?

/* Called when we must provide a list of factories to plug to @pad with @caps.* We first check if we have a sink that can handle the format and if we do, we* return NULL, to expose the pad. If we have no sink (or the sink does not* work), we return the list of elements that can connect. */
static GValueArray *
autoplug_factories_cb (GstElement * decodebin, GstPad * pad,GstCaps * caps, GstSourceGroup * group)
{GstPlayBin *playbin;GList *factory_list, *tmp;GValueArray *result;gboolean unref_caps = FALSE;gboolean isaudiodeclist = FALSE;gboolean isvideodeclist = FALSE;if (!caps) {caps = gst_caps_new_any ();unref_caps = TRUE;}playbin = group->playbin;GST_DEBUG_OBJECT (playbin, "factories group %p for %s:%s, %" GST_PTR_FORMAT,group, GST_DEBUG_PAD_NAME (pad), caps);/* filter out the elements based on the caps. */g_mutex_lock (&playbin->elements_lock);gst_play_bin_update_elements_list (playbin);//caps匹配的factory_listfactory_list =gst_element_factory_list_filter (playbin->elements, caps, GST_PAD_SINK,gst_caps_is_fixed (caps));g_mutex_unlock (&playbin->elements_lock);GST_DEBUG_OBJECT (playbin, "found factories %p", factory_list);GST_PLUGIN_FEATURE_LIST_DEBUG (factory_list);/* check whether the caps are asking for a list of audio/video decoders */tmp = factory_list;if (!gst_caps_is_any (caps)) {for (; tmp; tmp = tmp->next) {GstElementFactory *factory = (GstElementFactory *) tmp->data;isvideodeclist = gst_element_factory_list_is_type (factory,GST_ELEMENT_FACTORY_TYPE_DECODER |GST_ELEMENT_FACTORY_TYPE_MEDIA_VIDEO |GST_ELEMENT_FACTORY_TYPE_MEDIA_IMAGE);isaudiodeclist = gst_element_factory_list_is_type (factory,GST_ELEMENT_FACTORY_TYPE_DECODER |GST_ELEMENT_FACTORY_TYPE_MEDIA_AUDIO);if (isaudiodeclist || isvideodeclist)break;}}if (isaudiodeclist || isvideodeclist) {GSequence **ave_list;GstPlayFlags flags;if (isaudiodeclist)ave_list = &playbin->aelements;elseave_list = &playbin->velements;flags = gst_play_bin_get_flags (playbin);g_mutex_lock (&playbin->elements_lock);/* sort factory_list based on the GstAVElement list priority */factory_list = create_decoders_list (factory_list, *ave_list, flags);g_mutex_unlock (&playbin->elements_lock);}/* 2 additional elements for the already set audio/video sinks */result = g_value_array_new (g_list_length (factory_list) + 2);/* Check if we already have an audio/video sink and if this is the case* put it as the first element of the array */if (group->audio_sink) {GstElementFactory *factory = gst_element_get_factory (group->audio_sink);if (factory && _factory_can_sink_caps (factory, caps)) {GValue val = { 0, };g_value_init (&val, G_TYPE_OBJECT);g_value_set_object (&val, factory);result = g_value_array_append (result, &val);g_value_unset (&val);}}if (group->video_sink) {GstElementFactory *factory = gst_element_get_factory (group->video_sink);if (factory && _factory_can_sink_caps (factory, caps)) {GValue val = { 0, };g_value_init (&val, G_TYPE_OBJECT);g_value_set_object (&val, factory);result = g_value_array_append (result, &val);g_value_unset (&val);}}for (tmp = factory_list; tmp; tmp = tmp->next) {GstElementFactory *factory = GST_ELEMENT_FACTORY_CAST (tmp->data);GValue val = { 0, };if (group->audio_sink && gst_element_factory_list_is_type (factory,GST_ELEMENT_FACTORY_TYPE_SINK |GST_ELEMENT_FACTORY_TYPE_MEDIA_AUDIO)) {continue;}if (group->video_sink && gst_element_factory_list_is_type (factory,GST_ELEMENT_FACTORY_TYPE_SINK | GST_ELEMENT_FACTORY_TYPE_MEDIA_VIDEO| GST_ELEMENT_FACTORY_TYPE_MEDIA_IMAGE)) {continue;}g_value_init (&val, G_TYPE_OBJECT);g_value_set_object (&val, factory);g_value_array_append (result, &val);g_value_unset (&val);}gst_plugin_feature_list_free (factory_list);if (unref_caps)gst_caps_unref (caps);return result;
}

1.gst_play_bin_update_elements_list函數，創建可用的factories列表playbin->elements（?GList *elements; ?? /* factories we can use for selecting elements */）

/* Must be called with elements lock! */
static void
gst_play_bin_update_elements_list (GstPlayBin * playbin)
{GList *res, *tmp;guint cookie;cookie = gst_registry_get_feature_list_cookie (gst_registry_get ());if (!playbin->elements || playbin->elements_cookie != cookie) {if (playbin->elements)gst_plugin_feature_list_free (playbin->elements);res =gst_element_factory_list_get_elements(GST_ELEMENT_FACTORY_TYPE_DECODABLE, GST_RANK_MARGINAL);tmp =gst_element_factory_list_get_elements(GST_ELEMENT_FACTORY_TYPE_AUDIOVIDEO_SINKS, GST_RANK_MARGINAL);playbin->elements = g_list_concat (res, tmp);playbin->elements = g_list_sort (playbin->elements, compare_factories_func);}if (!playbin->aelements || playbin->elements_cookie != cookie) {if (playbin->aelements)g_sequence_free (playbin->aelements);playbin->aelements = avelements_create (playbin, TRUE);}if (!playbin->velements || playbin->elements_cookie != cookie) {if (playbin->velements)g_sequence_free (playbin->velements);playbin->velements = avelements_create (playbin, FALSE);}playbin->elements_cookie = cookie;
}

也就是同過gst_element_factory_list_get_elements從registry中獲取type是GST_ELEMENT_FACTORY_TYPE_DECODABLE,GST_ELEMENT_FACTORY_TYPE_AUDIOVIDEO_SINKS，優先級高于GST_RANK_MARGINAL的factory。

#define GST_ELEMENT_FACTORY_TYPE_DECODABLE \((GstElementFactoryListType)(GST_ELEMENT_FACTORY_TYPE_DECODER | GST_ELEMENT_FACTORY_TYPE_DEMUXER | GST_ELEMENT_FACTORY_TYPE_DEPAYLOADER | GST_ELEMENT_FACTORY_TYPE_PARSER | GST_ELEMENT_FACTORY_TYPE_DECRYPTOR))#define GST_ELEMENT_FACTORY_TYPE_AUDIOVIDEO_SINKS ((GstElementFactoryListType)(GST_ELEMENT_FACTORY_TYPE_SINK | GST_ELEMENT_FACTORY_TYPE_MEDIA_AUDIO | GST_ELEMENT_FACTORY_TYPE_MEDIA_VIDEO | GST_ELEMENT_FACTORY_TYPE_MEDIA_IMAGE))

還有(GSequence *)playbin->aelements和playbin->velements用來保存audioelement和videoelement。

（1）先看下gst_element_factory_list_get_elements

GList *
gst_element_factory_list_get_elements (GstElementFactoryListType type,GstRank minrank)
{GList *result;FilterData data;/* prepare type */data.type = type;data.minrank = minrank;/* get the feature list using the filter */result = gst_registry_feature_filter (gst_registry_get (),(GstPluginFeatureFilter) element_filter, FALSE, &data);/* sort on rank and name */result = g_list_sort (result, gst_plugin_feature_rank_compare_func);return result;
}//根據rank和type選擇
static gboolean
element_filter (GstPluginFeature * feature, FilterData * data)
{gboolean res;/* we only care about element factories */if (G_UNLIKELY (!GST_IS_ELEMENT_FACTORY (feature)))return FALSE;res = (gst_plugin_feature_get_rank (feature) >= data->minrank) &&gst_element_factory_list_is_type (GST_ELEMENT_FACTORY_CAST (feature),data->type);return res;
}//factory_type的判斷邏輯
gboolean
gst_element_factory_list_is_type (GstElementFactory * factory,GstElementFactoryListType type)
{gboolean res = FALSE;const gchar *klass;klass =gst_element_factory_get_metadata (factory, GST_ELEMENT_METADATA_KLASS);if (klass == NULL) {GST_ERROR_OBJECT (factory, "element factory is missing klass identifiers");return res;}/* Filter by element type first, as soon as it matches* one type, we skip all other tests */if (!res && (type & GST_ELEMENT_FACTORY_TYPE_SINK))res = (strstr (klass, "Sink") != NULL);if (!res && (type & GST_ELEMENT_FACTORY_TYPE_SRC))res = (strstr (klass, "Source") != NULL);if (!res && (type & GST_ELEMENT_FACTORY_TYPE_DECODER))res = (strstr (klass, "Decoder") != NULL);if (!res && (type & GST_ELEMENT_FACTORY_TYPE_ENCODER))res = (strstr (klass, "Encoder") != NULL);if (!res && (type & GST_ELEMENT_FACTORY_TYPE_MUXER))res = (strstr (klass, "Muxer") != NULL);if (!res && (type & GST_ELEMENT_FACTORY_TYPE_DEMUXER))res = (strstr (klass, "Demux") != NULL);/* FIXME : We're actually parsing two Classes here... */if (!res && (type & GST_ELEMENT_FACTORY_TYPE_PARSER))res = ((strstr (klass, "Parser") != NULL)&& (strstr (klass, "Codec") != NULL));if (!res && (type & GST_ELEMENT_FACTORY_TYPE_DEPAYLOADER))res = (strstr (klass, "Depayloader") != NULL);if (!res && (type & GST_ELEMENT_FACTORY_TYPE_PAYLOADER))res = (strstr (klass, "Payloader") != NULL);if (!res && (type & GST_ELEMENT_FACTORY_TYPE_FORMATTER))res = (strstr (klass, "Formatter") != NULL);if (!res && (type & GST_ELEMENT_FACTORY_TYPE_DECRYPTOR))res = (strstr (klass, "Decryptor") != NULL);if (!res && (type & GST_ELEMENT_FACTORY_TYPE_ENCRYPTOR))res = (strstr (klass, "Encryptor") != NULL);if (!res && (type & GST_ELEMENT_FACTORY_TYPE_HARDWARE))res = (strstr (klass, "Hardware") != NULL);/* Filter by media type now, we only test if it* matched any of the types above or only checking the media* type was requested. */if ((res || !(type & (GST_ELEMENT_FACTORY_TYPE_MAX_ELEMENTS - 1)))&& (type & (GST_ELEMENT_FACTORY_TYPE_MEDIA_AUDIO |GST_ELEMENT_FACTORY_TYPE_MEDIA_VIDEO |GST_ELEMENT_FACTORY_TYPE_MEDIA_IMAGE |GST_ELEMENT_FACTORY_TYPE_MEDIA_SUBTITLE |GST_ELEMENT_FACTORY_TYPE_MEDIA_METADATA)))res = ((type & GST_ELEMENT_FACTORY_TYPE_MEDIA_AUDIO)&& (strstr (klass, "Audio") != NULL))|| ((type & GST_ELEMENT_FACTORY_TYPE_MEDIA_VIDEO)&& (strstr (klass, "Video") != NULL))|| ((type & GST_ELEMENT_FACTORY_TYPE_MEDIA_IMAGE)&& (strstr (klass, "Image") != NULL)) ||((type & GST_ELEMENT_FACTORY_TYPE_MEDIA_SUBTITLE)&& (strstr (klass, "Subtitle") != NULL)) ||((type & GST_ELEMENT_FACTORY_TYPE_MEDIA_METADATA)&& (strstr (klass, "Metadata") != NULL));return res;
}//根據rank排序
gint
gst_plugin_feature_rank_compare_func (gconstpointer p1, gconstpointer p2)
{GstPluginFeature *f1, *f2;gint diff;f1 = (GstPluginFeature *) p1;f2 = (GstPluginFeature *) p2;diff = f2->rank - f1->rank;if (diff != 0)return diff;diff = strcmp (GST_OBJECT_NAME (f1), GST_OBJECT_NAME (f2));return diff;
}

（2）avelements_create，創建一個保存GstAudioVideoElement的GSequence?

/* The GstAudioVideoElement structure holding the audio/video decoder
?* and the audio/video sink factories together with field indicating
?* the number of common caps features */

static GSequence *
avelements_create (GstPlayBin * playbin, gboolean isaudioelement)
{GstElementFactory *d_factory, *s_factory;GList *dec_list, *sink_list, *dl, *sl;GSequence *ave_seq = NULL;GstAVElement *ave;guint n_common_cf = 0;//選擇符合要求的音視頻添加到對應的sink_list和dec_listif (isaudioelement) {sink_list = gst_element_factory_list_get_elements(GST_ELEMENT_FACTORY_TYPE_SINK |GST_ELEMENT_FACTORY_TYPE_MEDIA_AUDIO, GST_RANK_MARGINAL);dec_list =gst_element_factory_list_get_elements (GST_ELEMENT_FACTORY_TYPE_DECODER| GST_ELEMENT_FACTORY_TYPE_MEDIA_AUDIO, GST_RANK_MARGINAL);} else {sink_list = gst_element_factory_list_get_elements(GST_ELEMENT_FACTORY_TYPE_SINK |GST_ELEMENT_FACTORY_TYPE_MEDIA_VIDEO |GST_ELEMENT_FACTORY_TYPE_MEDIA_IMAGE, GST_RANK_MARGINAL);dec_list =gst_element_factory_list_get_elements (GST_ELEMENT_FACTORY_TYPE_DECODER| GST_ELEMENT_FACTORY_TYPE_MEDIA_VIDEO |GST_ELEMENT_FACTORY_TYPE_MEDIA_IMAGE, GST_RANK_MARGINAL);}/* create a list of audio/video elements. Each element in the list* is holding an audio/video decoder and an audio/video sink in which* the decoders srcpad template caps and sink element's sinkpad template* caps are compatible */dl = dec_list;sl = sink_list;ave_seq = g_sequence_new ((GDestroyNotify) avelements_free);//查找可以匹配的dec和sink，組合形式的ave，并保存到ave_seq，函數最后會返回/***** typedef struct*{*  GstElementFactory *dec;       /* audio:video decoder */*  GstElementFactory *sink;      /* audio:video sink */*  guint n_comm_cf;              /* number of common caps features */*} GstAVElement;*****/for (; dl; dl = dl->next) {d_factory = (GstElementFactory *) dl->data;for (; sl; sl = sl->next) {s_factory = (GstElementFactory *) sl->data;n_common_cf =gst_playback_utils_get_n_common_capsfeatures (d_factory, s_factory,gst_play_bin_get_flags (playbin), isaudioelement);if (n_common_cf < 1)continue;ave = g_slice_new (GstAVElement);ave->dec = gst_object_ref (d_factory);ave->sink = gst_object_ref (s_factory);ave->n_comm_cf = n_common_cf;g_sequence_append (ave_seq, ave);}sl = sink_list;}g_sequence_sort (ave_seq, (GCompareDataFunc) avelement_compare_decoder, NULL);gst_plugin_feature_list_free (dec_list);gst_plugin_feature_list_free (sink_list);return ave_seq;
}

主要看下gst_playback_utils_get_n_common_capsfeatures如何計算common caps features

  for (i = 0; i < fact1_caps_size; i++) {fact1_features =gst_caps_get_features ((const GstCaps *) fact1_tmpl_caps, i);if (gst_caps_features_is_any (fact1_features))continue;fact1_struct =gst_caps_get_structure ((const GstCaps *) fact1_tmpl_caps, i);for (j = 0; j < fact2_caps_size; j++) {fact2_features =gst_caps_get_features ((const GstCaps *) fact2_tmpl_caps, j);if (gst_caps_features_is_any (fact2_features))continue;fact2_struct =gst_caps_get_structure ((const GstCaps *) fact2_tmpl_caps, j);/* A common caps feature is given if the caps features are equal* and the structures can intersect. If the NATIVE_AUDIO/NATIVE_VIDEO* flags are not set we also allow if both structures are raw caps with* system memory caps features, because in that case we have converters in* place.*/if (gst_caps_features_is_equal (fact1_features, fact2_features) &&(gst_structure_can_intersect (fact1_struct, fact2_struct) ||(!native_raw&& gst_caps_features_is_equal (fact1_features,GST_CAPS_FEATURES_MEMORY_SYSTEM_MEMORY)&& gst_structure_can_intersect (raw_struct, fact1_struct)&& gst_structure_can_intersect (raw_struct, fact2_struct)))&& !is_included (cf_list, fact2_features)) {cf_list = g_list_prepend (cf_list, fact2_features);n_common_cf++;}}}

?2 .獲取factory_list ：查找包含sink_pad類型是caps匹配的elements

factory_list =
? ? ? gst_element_factory_list_filter (playbin->elements, caps, GST_PAD_SINK,
? ? ? gst_caps_is_fixed (caps));

GList *
gst_element_factory_list_filter (GList * list,const GstCaps * caps, GstPadDirection direction, gboolean subsetonly)
{GQueue results = G_QUEUE_INIT;GST_DEBUG ("finding factories");/* loop over all the factories */for (; list; list = list->next) {GstElementFactory *factory;const GList *templates;GList *walk;factory = (GstElementFactory *) list->data;GST_DEBUG ("Trying %s",gst_plugin_feature_get_name ((GstPluginFeature *) factory));/* get the templates from the element factory */templates = gst_element_factory_get_static_pad_templates (factory);for (walk = (GList *) templates; walk; walk = g_list_next (walk)) {GstStaticPadTemplate *templ = walk->data;/* we only care about the sink templates */if (templ->direction == direction) {GstCaps *tmpl_caps;/* try to intersect the caps with the caps of the template */tmpl_caps = gst_static_caps_get (&templ->static_caps);/* FIXME, intersect is not the right method, we ideally want to check* for a subset here *//* check if the intersection is empty */if ((subsetonly && gst_caps_is_subset (caps, tmpl_caps)) ||(!subsetonly && gst_caps_can_intersect (caps, tmpl_caps))) {/* non empty intersection, we can use this element */g_queue_push_tail (&results, gst_object_ref (factory));gst_caps_unref (tmpl_caps);break;}gst_caps_unref (tmpl_caps);}}}return results.head;
}

3.然后繼續后續處理，判斷找到factory_list中第一個audio/video decoder的位置

  /* check whether the caps are asking for a list of audio/video decoders */tmp = factory_list;if (!gst_caps_is_any (caps)) {for (; tmp; tmp = tmp->next) {GstElementFactory *factory = (GstElementFactory *) tmp->data;isvideodeclist = gst_element_factory_list_is_type (factory,GST_ELEMENT_FACTORY_TYPE_DECODER |GST_ELEMENT_FACTORY_TYPE_MEDIA_VIDEO |GST_ELEMENT_FACTORY_TYPE_MEDIA_IMAGE);isaudiodeclist = gst_element_factory_list_is_type (factory,GST_ELEMENT_FACTORY_TYPE_DECODER |GST_ELEMENT_FACTORY_TYPE_MEDIA_AUDIO);if (isaudiodeclist || isvideodeclist)break;}}if (isaudiodeclist || isvideodeclist) {GSequence **ave_list;GstPlayFlags flags;if (isaudiodeclist)ave_list = &playbin->aelements;elseave_list = &playbin->velements;flags = gst_play_bin_get_flags (playbin);//創建decoder_listg_mutex_lock (&playbin->elements_lock);/* sort factory_list based on the GstAVElement list priority */factory_list = create_decoders_list (factory_list, *ave_list, flags);g_mutex_unlock (&playbin->elements_lock);}

static GList *
create_decoders_list (GList * factory_list, GSequence * avelements,GstPlayFlags flags)
{GList *dec_list = NULL, *tmp;GList *ave_list = NULL;GList *ave_free_list = NULL;GstAVElement *ave, *best_ave;g_return_val_if_fail (factory_list != NULL, NULL);g_return_val_if_fail (avelements != NULL, NULL);for (tmp = factory_list; tmp; tmp = tmp->next) {GstElementFactory *factory = (GstElementFactory *) tmp->data;/* if there are parsers or sink elements, add them first */ //parsers or sink elements直接dec_list,如果不是走下面流程添加到ave_listif (gst_element_factory_list_is_type (factory,GST_ELEMENT_FACTORY_TYPE_PARSER) ||gst_element_factory_list_is_type (factory,GST_ELEMENT_FACTORY_TYPE_SINK)) {dec_list = g_list_prepend (dec_list, gst_object_ref (factory));} else if (!(((flags & GST_PLAY_FLAG_FORCE_SW_DECODERS) != 0) //如果沒有同時滿足以下兩個條件則為TRUE:強制軟件解碼且factory 是硬件解碼器類型&& gst_element_factory_list_is_type (factory,GST_ELEMENT_FACTORY_TYPE_HARDWARE))) {GSequenceIter *seq_iter;seq_iter =g_sequence_lookup (avelementszh, factory,(GCompareDataFunc) avelement_lookup_decoder, NULL);//avelements中查找，匹配條件avelement_lookup_decoderif (!seq_iter) {GstAVElement *ave = g_slice_new0 (GstAVElement);ave->dec = factory;ave->sink = NULL;/* There's at least raw */ave->n_comm_cf = 1;ave_list = g_list_prepend (ave_list, ave);/* We need to free these later */ave_free_list = g_list_prepend (ave_free_list, ave);continue;}/* Go to first iter with that decoder */do {GSequenceIter *tmp_seq_iter;tmp_seq_iter = g_sequence_iter_prev (seq_iter);if (!avelement_iter_is_equal (tmp_seq_iter, factory))break;seq_iter = tmp_seq_iter;} while (!g_sequence_iter_is_begin (seq_iter));/* Get the best ranked GstAVElement for that factory */best_ave = NULL;while (!g_sequence_iter_is_end (seq_iter)&& avelement_iter_is_equal (seq_iter, factory)) {ave = g_sequence_get (seq_iter);if (!best_ave || avelement_compare (ave, best_ave) < 0) //最佳匹配，匹配條件avelement_comparebest_ave = ave;seq_iter = g_sequence_iter_next (seq_iter);}ave_list = g_list_prepend (ave_list, best_ave);}}/* Sort all GstAVElements by their relative ranks and insert* into the decoders list */ave_list = g_list_sort (ave_list, (GCompareFunc) avelement_compare);for (tmp = ave_list; tmp; tmp = tmp->next) {ave = (GstAVElement *) tmp->data;dec_list = g_list_prepend (dec_list, gst_object_ref (ave->dec));//prepend是添加到list的頭部，所以需要后面的翻轉}g_list_free (ave_list);gst_plugin_feature_list_free (factory_list);for (tmp = ave_free_list; tmp; tmp = tmp->next)g_slice_free (GstAVElement, tmp->data);g_list_free (ave_free_list);//所以parse和sink都被添加到了前面，其他的根據rank等排序dec_list = g_list_reverse (dec_list);return dec_list;
}static gint
avelement_compare (gconstpointer p1, gconstpointer p2)
{GstAVElement *v1, *v2;GstPluginFeature *fd1, *fd2, *fs1, *fs2;gint64 diff, v1_rank, v2_rank;v1 = (GstAVElement *) p1;v2 = (GstAVElement *) p2;fd1 = (GstPluginFeature *) v1->dec;fd2 = (GstPluginFeature *) v2->dec;//優先比較sink的rank，沒有在比較dec的rank/* If both have a sink, we also compare their ranks */if (v1->sink && v2->sink) {fs1 = (GstPluginFeature *) v1->sink;fs2 = (GstPluginFeature *) v2->sink;v1_rank = (gint64) gst_plugin_feature_get_rank (fd1) *gst_plugin_feature_get_rank (fs1);v2_rank = (gint64) gst_plugin_feature_get_rank (fd2) *gst_plugin_feature_get_rank (fs2);} else {v1_rank = gst_plugin_feature_get_rank (fd1);v2_rank = gst_plugin_feature_get_rank (fd2);fs1 = fs2 = NULL;}/* comparison based on the rank */diff = v2_rank - v1_rank;if (diff < 0)return -1;else if (diff > 0)return 1;//比較number of common caps feature，多的優先/* comparison based on number of common caps features */diff = v2->n_comm_cf - v1->n_comm_cf;if (diff != 0)return diff;if (fs1 && fs2) {/* comparison based on the name of sink elements */diff = strcmp (GST_OBJECT_NAME (fs1), GST_OBJECT_NAME (fs2));if (diff != 0)return diff;}/* comparison based on the name of decoder elements */return strcmp (GST_OBJECT_NAME (fd1), GST_OBJECT_NAME (fd2));
}

這里注意下list中的排序吧：parse和sink最前，其他會按照優先級（rank）、共有 caps 特性數量、接收器名稱和解碼器名稱的順序排列。

后續如果應有sink則將sink插入到list中，基本也就完成了autoplug_factories_cb流程了。

?二、autoplug_select_cb

  GstPlayBin *playbin;GstElement *element;const gchar *klass;GstPlaySinkType type;GstElement **sinkp;GList *ave_list = NULL, *l;GstAVElement *ave = NULL;GSequence *ave_seq = NULL;GSequenceIter *seq_iter;gboolean created_sink = FALSE;{省略}  if (isaudiodec) {ave_seq = playbin->aelements;sinkp = &group->audio_sink;} else {ave_seq = playbin->velements;sinkp = &group->video_sink;}seq_iter =g_sequence_lookup (ave_seq, factory,(GCompareDataFunc) avelement_lookup_decoder, NULL);if (seq_iter) {/* Go to first iter with that decoder */do {GSequenceIter *tmp_seq_iter;tmp_seq_iter = g_sequence_iter_prev (seq_iter);if (!avelement_iter_is_equal (tmp_seq_iter, factory))break;seq_iter = tmp_seq_iter;} while (!g_sequence_iter_is_begin (seq_iter));while (!g_sequence_iter_is_end (seq_iter)&& avelement_iter_is_equal (seq_iter, factory)) {ave = g_sequence_get (seq_iter);ave_list = g_list_prepend (ave_list, ave);seq_iter = g_sequence_iter_next (seq_iter);}/* Sort all GstAVElements by their relative ranks and insert* into the decoders list */ave_list = g_list_sort (ave_list, (GCompareFunc) avelement_compare);} else {ave_list = g_list_prepend (ave_list, NULL);}